Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-18 GTBL042-Callister-v2 September 13, 2007 13:46

Revised Pages

744 • Chapter 18 / Magnetic Properties

Table 18.5 Typical Properties for Several Soft Magnetic Materials

Initial Saturation Flux Hysteresis

Composition Relative Density Bs Loss/Cycle Resistivity

Material (wt%) Permeabilityμi [tesla (gauss)] [J/m^3 (erg/cm^3 )] ρ(-m)

Commercial

iron ingot

99.95Fe 150 2.14 (21,400) 270 (2700) 1.0× 10 −^7

Silicon–iron

(oriented)

97Fe, 3Si 1400 2.01 (20,100) 40 (400) 4.7× 10 −^7

45 Permalloy 55Fe, 45Ni 2500 1.60 (16,000) 120 (1200) 4.5× 10 −^7

Supermalloy 79Ni, 15Fe, 5Mo, 0.5Mn 75,000 0.80 (8000) — 6.0× 10 −^7

Ferroxcube A 48MnFe 2 O 4 , 52ZnFe 2 O 4 1400 0.33 (3300) ∼40 (∼400) 2000

Ferroxcube B 36NiFe 2 O 4 , 64ZnFe 2 O 4 650 0.36 (3600) ∼35 (∼350) 107

Source:Adapted fromMetals Handbook: Properties and Selection: Stainless Steels, Tool Materials and Special-

Purpose Metals,Vol. 3, 9th edition, D. Benjamin (Senior Editor), American Society for Metals, 1980.

field. Using such a technique, a square hysteresis loop may be produced, which is

desirable in some magnetic amplifier and pulse transformer applications. In addi-

tion, soft magnetic materials are used in generators, motors, dynamos, and switching

circuits.

18.10 HARD MAGNETIC MATERIALS

Hard magnetic materials are utilized in permanent magnets, which must have a high

hard magnetic resistance to demagnetization. In terms of hysteresis behavior, ahard magnetic ma-

material terialhas a high remanence, coercivity, and saturation flux density, as well as a low

initial permeability, and high hysteresis energy losses. The hysteresis characteristics

for hard and soft magnetic materials are compared in Figure 18.19. The two most im-

portant characteristics relative to applications for these materials are the coercivity

and what is termed the “energy product,” designated as (BH)max. This (BH)maxcor-

responds to the area of the largestB-Hrectangle that can be constructed within the

second quadrant of the hysteresis curve, Figure 18.22; its units are kJ/m^3 (MGOe).^4

The value of the energy product is representative of the energy required to demag-

netize a permanent magnet; that is, the larger (BH)max, the harder is the material in

terms of its magnetic characteristics.

Again, hysteresis behavior is related to the ease with which the magnetic do-

main boundaries move; by impeding domain wall motion, the coercivity and suscep-

tibility are enhanced, such that a large external field is required for demagnetiza-

tion. Furthermore, these characteristics are interrelated to the microstructure of the

material.

(^4) MGOe is defined as
1 MGOe= 106 gauss-oersted
Furthermore, conversion from cgs–emu to SI units is accomplished by the relationship
1 MGOe= 7 .96 kJ/m^3